Everyone’s green energy journey is different. When it comes to residential solar, a little knowledge goes a long way towards designing a well-tailored system. In this article, we’ll review some of the practical considerations for homeowners shopping for solar panels for the first time.

Calculating how many solar panels you need

Solar panels are not created equally. The variables at play when comparing solar panels are power ratings and production ratios.

Production ratios account for normal performance fluctuations by pitting power ratings against output estimates based on real-world conditions such as peak sunlight hours, panel orientation, tilt and other elements. In areas with more sunlight, the resulting ratio will be higher. Solar panel installers may present these ratios when they provide you with an estimate.

For example: an 8000 W (8 kW) solar power system in Albany may produce 10,500 kWh in a year. Its production ratio would be 1.3.

10500 ÷ 8000 = 1.3

The same 8 kW system in San Jose could produce 12,000 kWh in a year, giving it a production ratio of 1.5.

12000 ÷ 8000 = 1.5

Meanwhile, power ratings refer to the maximum possible electricity output, in watts (W), of a single solar panel.

Formula to determine number of solar panels needed

Knowing the production ratio, power rating, and total desired output in kWh, you can calculate how many solar panels you need via the following formula:

system size ÷ production ratio ÷ panel power rating = no. of panels

To illustrate how this works, let’s assume the following:

  • Your family’s energy consumption is in line with the national average at around 10,500 kWh per year.
  • You live in upstate New York.
  • You’re considering buying an electric Kia Soul in the near future and want to install a home charging station for added convenience.

This vehicle requires 26 kWh of energy for every 100 miles. You don’t envision yourself driving more than 1,000 miles per month, which translates to a required solar capacity for 12,000 miles worth of charge. The calculations below translate this figure into 3,120 kWh per year.

12000 mi. ÷ 100 = 120

120 × 26 kWh = 3,120 kWh per year to charge

Adding 3,120 kWh of capacity to your current need of 10,500 kWh per year gives you a total system size of 13,620 kWh.

We already know that the production ratio you can expect in upstate New York is 1.3.

For power rating: solar panels typically produce 250 to 400 watts each. In this example, a 375 W model caught your eye as you were browsing.

13,620 kWh ÷ 1.3 ÷ 375 = 28 solar panels

This formula reveals that you’ll need 28 solar panels that will form part of a 10.5 kW system.

28 × 375 W = 10,500 W

Residential solar requires a significant upfront investment; almost all of the costs are incurred before switching on the panels. Crunching the numbers now will help you enjoy a predictable and enjoyable experience during those new and exciting first years while avoiding costly setbacks in the long run.

Perform an energy audit to understand your needs

To determine the amount and type of solar panels you need to purchase, you must determine your yearly electricity consumption. An easy way to do this is by referencing your utility bills, which indicate how many kilowatt hours (kWh) your household consumes. Add up the numbers from the last 12 months to get an idea of the minimum yearly production you’ll need from your panels.

If you’re moving into a new home that has appliances with which you’re unfamiliar, look up the machine’s Energy Guide info label to learn how many kWh it consumes per year, or use the Appliance Energy Calculator on energy.gov. Pay particular attention to items like pool pumps and central HVAC systems, as these tend to draw the most power.

This is also a great time to consider ways to reduce your energy consumption by finding inefficiencies. Sealing air leaks, upgrading insulation, and replacing incandescent light bulbs are just some of the steps you can take to ensure you’re not wasting electricity, which for solar users translates to increased energy independence.

Consider future energy consumption

It’s important to maximize the value of your initial investment in solar by obtaining enough panels to offset your energy needs as they increase over time. For instance, if you see yourself getting an electric car or spending more time at home in the future, now is the time to plan for this added capacity. Solar array design, installation, and permits come with fixed fees that you may need to pay again if you choose to expand your system later, reducing your possible financial gains. There’s also the possibility that your new panels will not match your old ones perfectly, which will negatively affect your home’s exterior aesthetics. If you have space to expand your proposed solar array and produce more electricity than you need right now, it’s worth considering.

Sunlight hours vary based on location

US solar exposure maps reveal that southwestern states are exposed to the most peak hours of sunlight in the nation, and areas in the northeast receive the least. While this impacts solar power production, it does not imply that residential solar is only a sound investment for people living in warmer climates. We compared the potential photovoltaic output in these two regions using the online Global Solar Atlas. Our findings indicate that while solar panels in San Jose, California could generate around 204 kWh per square foot (2,200 kWh per square meter) each year, the same system in Albany, New York could produce 149 kWh per square foot (over 1,600 kWh per square meter).

This means that folks living in areas further from the equator may need to increase photovoltaic coverage to produce equivalent power, or simply procure more powerful solar panels. The cost of these extra requirements may not significantly hamper return on investment when weighed against the money you can save on your utility bill, especially if you’re one of the many US homeowners spending in excess of $2,000 per year on electricity. Take a look at our economic benefits of residential solar blog post to learn more.










Photo by Gus Ruballo on Unsplash